Boundary Change Map

I pulled together this interactive map of Proposed Constituency Boundary Changes in England, after the information was released by the Boundary Commission for England last week. My colleague James Cheshire highlighted that this kind of map could be illuminating, particularly as the official maps are simple greyscale PDFs of each new constituency boundary, without the old boundaries or adjoining constituencies for context, and with one document per constituency!

Click the image above to go to the interactive map, then use the slider to fade between the current and proposed boundaries. The new boundaries have been put together to have roughly the same populations in each one (72000-80000 people), and also the total number of constituencies has been dropped by around 5-10%. They are just proposed ones, and are themselves revised from an earlier version.

There are some interesting patterns – many urban areas, such as London, have undergone very significant redrawings, while many rural areas – historically with higher constituency populations – remain untouched. For example, Tottenham loses its identity as a single constituency, the southern half being assimulated into Stamford Hill and the northern half into Edmonton. Slough has a big bite taken out of its SW corner, the people here potentially being represented by a Windsor MP in the future. Much of north Yorkshire is unchanged however.

We didn’t use vector-based boundaries here, even though this would have made it more interactive, because of the size of the boundary files – simplifying them to reduce the size would have been tricky (as it would have made unmoved boundaries move slightly) and the necessary simplification might have distorted the boundaries too much.

As with all my more recent web visualisations, social media (Twitter and Facebook) buttons are included, and geolocation is used to default the view to the user’s location, if they are in England.

On a technical note, this is my first pure HTML5 map. It also takes advantage of simpler ways of setting up maps in the latest release of OpenLayers, 2.12. It means it is out-of-the-box compatible with mobile browsers, and the HTML, JavaScript (including a JQueryUI slider) and CSS adds up to less than 200 lines of code – the only other code used being a couple of Mapnik XML stylesheets for rendering the two maps themselves.

Thanks to James Cheshire for the idea and getting hold of the data.